The present invention relates to a nonaqueous electrolyte battery comprising a positive electrode having a positive electrode active material, a negative electrode containing a negative electrode active material capable of being doped/undoped with lithium, and a nonaqueous electrolyte.
Progress in electronic technology has led to the development of various types of small and portable high-performance electronic devices. Accordingly, batteries for operating these electronic devices are required to be light-weight and of high-capacity, and energy density thereof needs to be further improved.
As the batteries for driving these electronic devices, secondary batteries such as nickel-cadmium batteries, lead batteries, and so forth have been conventionally used. However, these batteries have a low discharge potential and fail to obtain a desired energy density.
Presently, research and development on the nonaqueous electrolyte secondary battery having a negative electrode composed of lithium or a lithium alloy is being conducted widely.
This type of battery has a high energy density and a low self-discharge, and is light-weight because a lithium containing composite oxide having a high discharge voltage, typically LiCoO2, is used as the material of the positive electrode. However, when the nonaqueous electrolyte secondary battery has a negative electrode composed of lithium or a lithium alloy, lithium dendrite grows and reaches the positive electrode during repeated charge/discharge cycles, causing short-circuits inside the battery. Moreover, when quick a charge/discharge is performed as in the case of actual use, dendrite is generated inside the battery, making the battery unusable.
Consequently, a nonaqueous electrolyte battery using a negative electrode active material which is capable of occluding lithium ions in an intercalation compound, such as a metal oxide or carbon, and which is capable of being doped/undoped with lithium without depositing lithium on the negative electrode, i.e., a so-called lithium-ion battery, has drawn wide attention. In this lithium-ion secondary battery, lithium dendrite does not precipitate, even when the charge/discharge cycle is repeated, and superior charge/discharge cycle characteristics can be obtained.
Because of these advantages, lithium-ion secondary batteries have come to be used in various fields as the power sources of various electronic devices, especially portable devices.
Among portable electronic devices, cellular phones, for example, are used repetitively and perpetually consume electricity. Consequently, the secondary batteries used as the power sources of these portable electronic devices undergo a frequent charge and discharge.
When the lithium-ion secondary battery is frequently charged and discharged, the battery capacity thereof is degraded due to the irreversible reactions occurring between the negative electrode and the nonaqueous electrolyte. As a result, the lithium-ion secondary battery suffers from a short cycle life.